A monomolecular film may be formed by a chemical adsorption process as is well known in the art.
The principles underlying the manufacture of a chemically adsorbed monomolecular film reside in forming a monomolecular film by making use of a hydrochloric acid removal reaction between hydroxyl groups on a substrate surface and chlorosilyl groups of a chlorosilane-based surface active agent.
It has been impossible to form a film on a substrate which has no hydroxyl group present on the surface, such as a plastic substrate.
Further, with a substrate having hydroxyl groups present at a low density on the surface, such as aluminum and stainless steel substrates, it is impossible to form a perfect adsorption film in a short period of time because of the low density of hydroxyl groups.
Accordingly, to form a chemically adsorbed film on the surface of an aluminum or stainless steel substrate, the surface of the substrate has, in practice, been oxidized to introduce hydroxyl groups.
Meanwhile, the surface of an aluminum or stainless steel substrate is rendered heat-resistant, weather-resistant and wear-resistant by coating the substrate surface with a fluorocarbon-based thin film.
This is usually done by rendering the surface of an aluminum substrate, or the like, coarse by means of a wire brush or chemical etching, coating with a primer or the like and then with a paint prepared by suspending fluorocarbon-based fine particles of ethylene polytetrafluoride or the like in ethanol or the like, followed by drying and then baking at 400.degree. C. for about one hour, thus fixing a fluorocarbon-based polymer on the substrate surface.
The prior art method, in which the surface of an aluminum or stainless steel substrate is oxidized to introduce hydroxyl groups to the substrate surface so as to obtain a perfect chemically adsorbed film, however, does not have a substantially high effect of increasing hydroxyl groups. Typically, the formation of a perfect adsorption film requires an adsorbing operation at room temperature for about 100 hours. Besides, the substrate surface becomes coarse.
The prior art method of manufacturing (or coating) a fluorocarbon-based coating film, on the other hand, permits ready formation of the film. However, since the polymer is in close contact with the substrate with the sole anchoring effect, is a limit on the close contact of the polymer with the substrate. Therefore, the performance of the method is insufficient when used for manufacturing high mechanical strength apparatuses and the like requiring heat-resistant, weather-resistant and wear-resistant coatings, for instance hot plates, rice cookers and other electric products, vehicles, industrial machines, glass lenses and mirrors.
Moreover, with the prior art coating method a coating film thickness of at least several ten microns is necessary in order to prevent generation of pin-holes.